Intrinsic gauging for tube fittings

ABSTRACT

An intrinsic gauging device for a ferrule type tube fitting of the type having a coupling nut, a coupling body and at least one ferrule, includes a precisely formed marking on the coupling body that is visually perceptible when the coupling is in a finger tight position, and that is covered or visually imperceptible or otherwise has a predetermined relationship with the coupling nut when the fitting has been initially pulled-up. In a preferred form, the marking is realized as a precision groove or recess machined into a surface of the coupling body. The groove can be made more easily visually perceptible such as by roughening or knurling the surface, or coloring the surface, for example. The groove defines an edge at a precise position that corresponds to a predetermined axial displacement of the nut relative to the body for initial pull-up. The marking may also be formed with a precise dimension such as an axial length to provide a second edge that corresponds to a predetermined axial displacement of the nut relative to the body beyond initial pull-up for fitting assemblies that are remade.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to tube fittings of the type thatuse one or more ferrules for gripping a tube end. More particularly, theinvention relates to an intrinsic gauging apparatus and method forvisual verification that the fitting has been properly pulled up.

BACKGROUND OF THE INVENTION

[0002] Ferrule-type tube fittings are well known in the art. A twoferrule fitting that has been highly successful for over 30 years is asequential gripping arrangement invented by Lennon, et al., U.S. Pat.No. 3,103,373, the entire disclosure of which is fully incorporatedherein by reference.

[0003] In a typical ferrule-type tube fitting assembly there is acoupling arrangement that includes a coupling body and a coupling nutthat is threadably engaged with threads on one end of the coupling body.The coupling body includes a torquing flange, typically in the form of ahex shaped flange. The coupling body at the other end may be joined toor integral with another body, flow control device and so on. Thecoupling body includes an axially tapered opening or camming mouth and ashoulder or stop axially spaced from the tapered opening. Two grippingcomponents or ferrules, including a rear ferrule and a front ferrule,are positioned within the coupling nut and are interposed between thecoupling body and the coupling nut. The tapered front end of the frontferrule initially engages the camming mouth of the coupling body and atapered front end of the rear ferrule initially engages a cammingsurface at the back end of the front ferrule. The coupling nut has ashoulder that drivingly engages a back wall of the rear ferrule. A tubeend is axially inserted into the fitting until the tube end abuts theinner shoulder stop of the coupling body. Upon relative rotation of thecoupling body and nut which drives the coupling components axiallytowards each other, the tapered ferrules are axially pulled together,commonly referred to in the art as being “pulled-up”, and radiallydisplaced inwardly to cause a sequential inward gripping of the tube.The ferrules tightly grip the tube wall due to the swaging action.

[0004] Typically, a tube fitting assembly such as described above, isshipped to a customer in an assembled condition with the ferrulesinstalled in the coupling nut and the coupling nut threaded onto thecoupling body to a finger tight condition. The assembler then slips atube end axially into the fitting until it bottoms or abuts the innerstop shoulder on the coupling body. With the fitting in an initialfinger tight condition, the assembler, using a wrench or spanner or thelike for example, then imparts a relative rotation between the couplingbody and the coupling nut for a predetermined rotation to complete theinstallation. For smaller tube fittings, for example tube fittings usedon one-quarter (¼) to one (1) inch tubing, there is typically a relativerotation of one and a quarter “turns past finger tight” (“TPFT”)position to achieve proper initial pull-up.

[0005] The number of turns to properly pull-up a fitting assembly isdetermined by a number of factors including the thread pitch and theproper axial displacement of the coupling nut relative to the couplingbody to insure that the ferrules are properly swaged onto the tube wall.Although the various parts of the fitting are machined with highprecision and assembled to a finger tight position, it still can bedifficult to keep track of the number of rotations and fractions thereofto pull-up the fitting. Many times the fitting is being installed in anarea with limited clearance for the wrench, thus necessitating a numberof separate wrenching operations for one complete rotation.

[0006] A successful and commonly used solution to verifying properpull-up is a NO-GO gauge as described in U.S. Pat. No. 3,287,813 toLennon et al., the entire disclosure of which is fully incorporatedherein by reference. This gauge effectively verifies that the gap orrelative spacing between the coupling body flange and the forward end ofthe coupling nut is of the correct dimension. The assembler firstimparts the required relative rotation between the coupling nut andbody. If the gauge cannot fit between the body and the coupling nut, theassembler knows that the nut has at least been properly pulled-up.

[0007] Although the gauging tool described above continues to enjoyexcellent commercial success and use, there are applications where theuse of the gauge may be an inconvenience. Of particular interest is theneed for a gauge that does not necessarily require a separate gaugetool, but rather could be intrinsically part of the fitting.

[0008] Additionally, the NO-GO gauge is used principally for initialpull-up of the fitting assembly. In some cases, a coupling may bedisassembled by unthreading the coupling nut from the body for repair orreplacement of the device joined to the tube end. During remake of thefitting, typically the relative rotation between the coupling nut andbody requires fractionally more turns than is required for initialpull-up, or in other words the axial displacement of the coupling nuttowards the coupling body is slightly greater each pull-up compared tothe previous pull-up operation. A manufacturer may determine arecommended number of remakes based on various design factors andempirical data to limit the axial displacement of the coupling nut withrespect to the coupling body to a predetermined amount beyond theinitial pull-up axial displacement. The design factors taken intoconsideration may include the pressure and temperature ratings for thefitting, the materials used in the tubing and the fitting components andso on.

[0009] The actual number of remakes a given fitting assembly canactually undergo and still exhibit acceptable performancecharacteristics may be significantly higher than the recommended numberof remakes, but it is still desirable in some cases to be able toprovide an indication to the assembler that the fitting assembly hasbeen remade a number of times so as to have advanced the coupling nutand body together a predetermined axial displacement beyond initialpull-up. Since the hand gauge discussed above necessarily has a fixedaxial dimension, it is not useful for verifying remade fittings.

[0010] It is therefore an objective of the present invention to anintrinsic gauging device and method for verifying proper pull-up of aferrule-type tube fitting for initial pull-up. It is another objectiveto provide an intrinsic gauging device and method that verifies properinitial pull-up and also can be used to provide an indication that thefitting has been remade a number of times so as to indicate apredetermined axial displacement of the coupling nut relative to thecoupling body.

SUMMARY OF THE INVENTION

[0011] To the accomplishment of the aforementioned and other objectives,and in accordance with one embodiment of the invention, an intrinsicgauging device includes a precisely formed and positioned marking on thecoupling body that is visually perceptible when the coupling is in afinger tight position, and that is covered or visually imperceptiblewhen the fitting has been properly pulled-up. In a preferred form, themarking is realized as a precision groove or recess machined into asurface of the coupling body. The groove can be made more visuallyperceptible such as by roughening or knurling the surface, or coloringthe surface, for example. Use of the intrinsic gauge thus avoids theneed to count or remember the number of relative rotations andfractional rotations imparted to the coupling nut and body. The positionof the marking corresponds to a predetermined axial displacement of thecoupling nut relative to the coupling body for initial pull-up.

[0012] The invention further contemplates the methods embodied in theuse of such an intrinsic gauging device, as well as in anotherembodiment, a method for gauging proper pull-up of a coupling nut on acoupling body in a ferrule type fitting, the method including the stepsof positioning a visually perceptible marking on the coupling body;forming the marking with an axial length that corresponds to apredetermined axial displacement of the coupling nut relative to thecoupling body; assembling the fitting to a finger tight condition; andtightening the coupling nut onto the coupling body until the marking isjust hidden from view by the nut.

[0013] In accordance with another aspect of the invention, the markingmay be formed with a predetermined axial dimension and precisely locatedon the coupling body so that upon proper initial pull-up the couplingnut aligns with a leading edge of the marking; and upon a predeterminedadditional axial displacement of the coupling nut relative to thecoupling body during subsequent remakes, the nut covers the marking oraligns with a trailing edge of the marking.

[0014] These and other aspects and advantages of the present inventionwill be apparent to anyone skilled in the art from the followingdescription of the preferred embodiments in view of the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The invention may take physical form in certain parts andarrangements of parts, preferred embodiments and a method of which willbe described in detail in this specification and illustrated in theaccompanying drawings which form a part hereof, and wherein:

[0016]FIG. 1 is a ferrule-type fitting that incorporates an intrinsicgauge feature in accordance with the invention, the fitting being shownin longitudinal cross-section in a finger tight position; and

[0017]FIG. 2 is the fitting of FIG. 1 shown in a proper pulled-upcondition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] With reference to FIG. 1, the invention will be described hereinin an exemplary manner as being incorporated into a standard two ferrulestyle tube fitting assembly. However, this description is intended to beexemplary in nature to explain and illustrate the concepts andadvantages of the present invention, and therefore should not beconstrued in a limiting sense. Persons of mere ordinary skill in the artwill readily understand and appreciate that the invention can be put topractice in a wide variety of tube fittings and couplings that utilizetwo components that are relatively rotated to make up the assembly. Forexample, and not for purposes of limitation, the present invention canconveniently be used in a single ferrule tube fitting or with any twopart coupling in which proper assembly is determined in part by accuraterelative rotation between two threaded parts.

[0019] The standard fitting assembly 10 includes a coupling body 12 anda coupling nut 14. The coupling body 12 includes a first end 16 that isexternally threaded as at 18. The coupling nut is internally threaded asat 20 and the nut 14 can be easily installed on the coupling body 12 byrelative rotation between the body 12 and the nut 14. The term“relative” rotation is used herein because although a typical assemblyprocedure for the fitting 10 involves restraining the body 12 againstrotation and turning the nut 14 with a wrench, such a procedure is notrequired to practice the present invention. It is contemplated that thebody 12 could be rotated while holding the nut 14 stationary, oralternatively, rotational movement could be applied to both the nut andbody to rotate them in opposite directions at the same time to make upthe fitting 10. The body and nut are typically provided with hex shapedportions 22, 24 respectively to assist in the use of a wrench or othertool to impart the relative rotation.

[0020] The threaded end 16 of the body 12 has a central bore orpassageway 26 that extends longitudinally all the way through thecoupling body 12. This bore 26 is formed with a tapered camming mouth 28at the forward end of the coupling body 12. The coupling body 12includes an inner shoulder 30 such as a counterbore that is axiallyspaced from the camming mouth 28.

[0021] The fitting assembly 10 further includes a front ferrule 32 and arear ferrule 34. The front ferrule 32 has a tapered nose portion 36 thatengages the tapered camming mouth 28 of the coupling body 12. The frontferrule 32 also is formed with a tapered camming mouth 38 at the backend thereof. The rear ferrule 34 includes a tapered nose portion 40 thatengages the tapered camming mouth 38 of the front ferrule 32. All of thefitting 10 components are commercially available from Swagelok Company,Solon, Ohio.

[0022] The fitting assembly 10 is illustrated in FIG. 1 in the “fingertight position” or FTP as the fitting would typically be received fromthe manufacturer. The drawing also illustrates the fitting 10 after atube end A has been inserted into the fitting 10. Since the couplingcomponents 12, 14 are only finger tight, the tube end A easily slidesinto the fitting assembly 10 until the tube end wall B abuts the innershoulder 30 of the coupling body 12. The front and rear ferrules 32, 34both have generally cylindrical bores 32 a and 34 a respectively thatare closely received about the tubing outer wall C.

[0023] It is important to note that the present invention is not limitedto the ferrule geometry illustrated in the drawings. Many differentferrule configurations can be used with the present invention.

[0024] The coupling nut 14 includes an inwardly extending shoulder 42that serves as a driving surface that engages the back wall 34 b of therear ferrule 34. As the coupling nut 14 is tightened down onto thecoupling body 12, the rear ferrule 34 is driven forward into the cammingmouth at the back end of the front ferrule 32 and a sequential grippingoperation takes place as described in the above referenced patents tocause inward radial displacement of the ferrules 32, 34 to swage theminto a strong and fluid tight grip on the tube wall C (see FIG. 2).

[0025] The relative axial displacement of the coupling nut 14 onto thecoupling body 12 is related to the number of complete and fractionalrelative rotations between the body 12 and the nut 14. The nut 14 isadvanced far enough relative to the body 12 to impart a strong grippingaction by the ferrules 32, 34 on the tube wall C. Accordingly, a typicalassembly instruction would indicate the number of full and fractionalturns to impart, for example, to the coupling nut 14 while holding thecoupling body 12 stationary.

[0026] As technology advances in the materials and design of the fitting10 components, the torque needed to make up the fitting 10 tends todecrease. For example, this decrease in make-up torque can result fromimprovements that reduce galling between the nut 14 and the rear ferrule34. Whatever the reason may be, reduced torque makes it easier for anassembler to inadvertently advance the nut 14 axially beyond the pointsufficient for initial pull-up of the fitting 10. Over advancing the nut14 relative to the body 12 beyond this point is typically accommodatedby the fitting design due to the desirability in some applications topermit remakes. However, such over advancing of the nut 14 onto the body12 during initial pull-up reduces the additional relative axialdisplacement available for subsequent remakes, which thus in turnreduces the available number of remakes.

[0027] In accordance with a feature of the invention, an intrinsicgauging device is provided on the coupling body 12. By “intrinsicgauging” is simply meant that the gauge device and/or function ormethodology is inherently embodied in one or more of the fittingcomponents and therefore can be used without any external or separategauging tool. In the preferred but not required form, the intrinsicgauge is realized as a precisely positioned visually perceptible markingon the coupling body 12. In this exemplary embodiment, the marking is aprecision machined groove or recess 50 formed in the coupling body neck52. More preferably, the groove 50 is positioned adjacent to or near theend thread 54 of the threaded body 12. The groove 50 has a leading edge50 a and a trailing edge 50 b. The groove 50 is visually perceptible toan assembler when the fitting is in the FTP as illustrated in FIG. 1.The groove 50 is preferably but again not necessarily circumferential.Alternatively, the groove 50 could be formed in arcuate sections aboutthe body neck 52. Virtually any geometric shape could be machined intothe body 12 to form the marking 50 so long as it has a well defined andvisually perceptible edge or edges or other suitable demarcation, aswill be apparent from the following discussion.

[0028] The axial position 56 of the trailing edge 50 b of the groove 50is precisely machined so that when the fitting 10 has been properly andinitially pulled-up, as illustrated in FIG. 2, the coupling nut forwardend 14 a substantially aligns with the edge 50 b and the nut 14substantially obstructs visual perception of the groove 50, particularlyfrom a lateral viewing angle relative to the longitudinal axis X of thefitting 10. The precise location and positioning of the trailing edge 50b is used as a marker so that the assembler can pull-up the fitting 10by advancing the coupling nut 14 relative to the coupling body 12 to theproper initial position, referred to herein as the “predeterminedinitial pull-up”. This predetermined initial pull-up conditioncorresponds to a predetermined initial axial position of the nut 14relative to the body 12 for initial pull-up to swage the ferrules 32, 34onto the tube wall C. To aid in the visual perception of the groove 50before the assembly is in the pulled-up condition, the groove 50 can becolored as by applying a paint or other coloring material to thevisually perceptible surface, such as the bottom groove surface 58. Forexample, an adhesive strip with a suitable color can be placed in thegroove 50. Still further, the groove surface 58 could be knurled orotherwise changed in texture or appearance to be easily seen to thehuman eye. Further still, a snap ring may be installed into the groove50.

[0029] Still as another alternative to forming a groove 50, a machinedband could be formed in or on the neck 52, such as again by knurling,stippling, roughening and so forth.

[0030] For the initial pull-up gauging aspect of the invention, the useof a groove improves visual perception of the edge 50 b. Those skilledin the art will readily appreciate that the marking 50 may be realizedin the form of any suitable edge, line or other demarcation eitherraised or recessed in the coupling body 12 that is visually perceptibleduring pull-up to indicate to the assembler that the predeterminedinitial pull-up position has been reached and therefore furtheradvancing of the nut 14 is no longer required. Of course, the assemblercan still rotate the nut 14 past this position, but in any case theintrinsic gauge has provided the indication that the nut 14 has beenpulled up to at least the initial pull-up position.

[0031] As an exemplary assembly procedure and method for intrinsicgauging, the assembler installs the tube end A into the fitting. Using awrench or other suitable tool the coupling body 12 is held stationaryand the coupling nut 14 rotated until the marking 50 is just obstructedfrom view. For embodiments that use a simpler demarcation for themarking 50, the nut 14 is rotated until the edge 14 a of the nutsubstantially aligns with the marking 50. Therefore, with the presentinvention there is no need to count or keep track of the number ofcomplete and fractional relative rotations between the body 12 and thenut 14.

[0032] For fittings 10 that will be made and remade, the leading edge 50a can also be precisely axially positioned so that in the FTP theleading edge 50 a will be axially spaced from the forward end 14 a ofthe nut 14. The leading edge 50 a is positioned such that when theproper pull-up has been effected, the forward end 14 a of the nut 14aligns with the leading edge 50 a. During subsequent remakes, the nut 14advances a little further each time to achieve proper pull up. After apredetermined number of remakes the forward end 14 a of the nut 14aligns with the trailing edge 50 b of the marking 50, therebysubstantially covering the marking 50, and the assembler knows that thefitting 10 has been remade to the point where the coupling nut 14 hasbeen axially advanced a predetermined amount relative to the couplingbody 12 past the initial pull-up condition. The axial length between theleading and trailing edges 50 a, 50 b of the marking 50 can bedetermined from design analysis and empirical data so that the marking50 becomes covered by the nut 14 after a number of remakes thatcorresponds to a predetermined advance of the coupling nut 14 relativeto the coupling body 12 beyond the predetermined initial pull-upposition.

[0033] Regardless of its form, the marking 50 can be precisely machinedbased on the machining profile of the body 12 so that the markingprovides an accurate and permanent visually perceptible indicia fordetermining proper pull-up of the fitting 10.

[0034] The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon a reading and understanding of this specification. It isintended to include all such modifications and alterations insofar asthey come within the scope of the appended claims or the equivalentsthereof

Having thus described the invention, it is claimed:
 1. Intrinsic gaugingassembly for a ferrule type tube fitting, comprising: a coupling bodyhaving a threaded end that is capable of receiving a tube end; athreaded coupling nut that mates with said threaded end of the couplingbody; at least one ferrule retained in the nut interior; and a visuallyperceptible marking on the coupling body that is visible when thefitting is in a finger tight condition, and that is substantiallyimperceptible after the fitting has been assembled on a tube end to aninitial pull-up position.
 2. The assembly of claim 1 wherein saidmarking comprises a machined surface on the coupling body.
 3. Theassembly of claim 2 wherein said marking is adjacent said threaded endof the coupling body.
 4. The assembly of claim 2 wherein said machinedsurface is knurled.
 5. The assembly of claim 1 wherein said marking hasan axial position that corresponds to a predetermined axial advance ofthe coupling nut relative to the coupling body for initial pull-up. 6.The assembly of claim 1 wherein said marking comprises a machined recessin a neck portion of said coupling body.
 7. The assembly of claim 1wherein said marking comprises a machined recess in said coupling body.8. The assembly of claim 1 wherein marking comprises a band having apredetermined axial length.
 9. The assembly of claim 1 wherein saidmarking comprises a colored machined groove.
 10. The assembly of claim 1wherein said marking comprises at least two demarcations on saidcoupling body to form a leading and trailing marking edge; said leadingedge corresponding to a predetermined initial pull-up of the assemblyand said trailing edge corresponding to an additional predeterminedaxial displacement of said nut relative to said body beyond said initialpull-up.
 11. The assembly of claim 1 wherein said marking comprises ademarcation that is axially positioned on said body and corresponds to apredetermined axial displacement of said nut relative to said body forinitial pull-up.
 12. The assembly of claim 11 wherein said demarcationcomprises an edge that substantially aligns with a forward end of saidcoupling nut when the nut has been axially displaced relative to thebody by said predetermined axial displacement for initial pull-up. 13.The assembly of claim 11 wherein said demarcation is substantiallyobstructed from view after the nut has been axially displaced relativeto the body by at least said predetermined displacement for initialpull-up.
 14. Intrinsic gauge for a ferrule type tube fitting assembly,comprising: a coupling body having a threaded end that can receive atube end and at least one ferrule and that can be mated with a couplingnut as a fitting assembly; said coupling body having a visuallyperceptible marking thereon that is visible when the fitting assembly isin a finger tight condition, and that has a predetermined relationshipto the coupling nut when the fitting assembly has been properly pulledup on a tube end; said marking corresponding to a predetermined axialdisplacement of the nut relative to the body for initial pull-up. 15.The assembly of claim 14 wherein said marking comprises a machinedsurface on the coupling body.
 16. The assembly of claim 15 wherein saidsurface is adjacent a back end of said threaded end of the couplingbody.
 17. The assembly of claim 15 wherein said machined surface isknurled.
 18. The assembly of claim 14 wherein said marking has apredetermined axial length defined by two demarcations, a firstdemarcation corresponding to a predetermined axial displacement of thecoupling nut relative to the coupling body for initial pull-up and asecond demarcation corresponding to an additional axial displacement ofthe nut relative to the body beyond said initial pull-up.
 19. A methodfor gauging proper pull-up of a coupling nut on a coupling body in aferrule type fitting, comprising the steps of: a. forming a visuallyperceptible marking on the coupling body; b. said forming stepcomprising positioning the marking to correspond to a predeterminedaxial displacement of the coupling nut relative to the coupling body forinitial pull-up; and c. assembling the coupling nut onto the couplingbody until the marking corresponds with the nut.
 20. The method of claim19 wherein the step of forming the marking comprises the step ofmachining a groove in the coupling body.
 21. The method of claim 20wherein the step of forming the marking comprises the step of applying acolor surface to said groove.
 22. The method of claim 20 wherein thestep of forming the marking comprises the step of knurling the surfaceof said groove.
 23. The method of claim 19 comprising the step ofimparting relative rotation between the nut and body to produce an axialdisplacement of the nut relative to the body until said marking issubstantially visually obstructed.
 24. The method of claim 19 whereinthe step of forming the marking comprises the step of forming at leasttwo demarcations on the coupling body; and forming said demarcations asa leading edge and a trailing edge wherein the leading edge correspondsto axial displacement of the nut relative to the body for initialpull-up of the fitting and the trailing edge corresponds to anadditional axial displacement of the nut relative to the body beyond theinitial pull-up.